ADSORPTION OF CHARGED BLOCK-COPOLYMERS - EFFECT ON COLLOIDAL STABILITY

We study the effect on colloidal stability of the adsorption of diblock copolymers with a charged buoy block. Using a scaling as well as an SCF approach, we focus on the high-charge regime and find that adsorbed amounts are very low. Nevertheless, the adsorbed polymer causes a significant repulsive interaction between two surfaces. For low charges and long anchor blocks (''anchor-dominated regime'') the colloidal stability would be expected to rise with increasing charge on the buoy block. In our high-charge regime we find the reverse; i.e., the electrosteric repulsive interaction increases with increasing salt concentration and decreasing buoy length or buoy charge. This counterintuitive behavior is caused by the effect of the electrostatic interactions on the adsorbed amount: stronger interactions lead to a lower adsorbed amount, which in turn leads to a weaker repulsion. Numerical SCF calculations confirm these scaling predictions.